Aircraft undercarriages are known that include a bottom portion that is steerable and a steering member adapted to turn the steerable bottom portion in response to a steering order.
The steering member often includes one or more actuators which act on the steerable bottom portion. Other types of steering member are known, e.g. using a rack.
In the field of carrier-borne aircraft, it is known to use steering members that include an actuator with a hydraulic motor co-operating with a toothed ring secured to the steerable bottom portion of the undercarriage.
In the field of light aircraft, it is known to use a steering member including an actuator with an electric motor co-operating with a toothed ring secured to the steerable bottom portion of the undercarriage.
Nevertheless, if the actuator member fails, command over steering is lost completely, and it is no longer possible to direct the aircraft under its own control other than by differential braking or by asymmetrical thrust from its engines.